The targeting of neurotransmitter receptors to synapses is essential for efficient synaptic transmission and plays an important role in the regulation of synaptic plasticity in the brain. We have identified several PDZ domain-containing proteins that specifically interact with AMPA receptors, the major excitatory neurotransmitter receptors in the central nervous system. These AMPA receptor interacting proteins are critical for the regulation of the membrane trafficking of AMPA receptors and synaptic plasticity. Several of these proteins, including GRIP1 and GRIP2 (Glutamate Receptor Interacting Proteins) and PICK1 (Protein Interactor with C Kinase), specifically interact with the C-terminal domains of the AMPA receptor GluR 2, 3 and 4c subunits. In addition, we have found that these interactions are dynamically regulated by protein phosphorylation of the receptor subunits. In this research proposal we plan to use several complementary approaches to further characterize the structure and function of PICK1 and GRIP1/2 and determine their roles in AMPA receptor synaptic targeting, synaptic plasticity and behavior. First, we have identified several novel proteins that interact with PICK1 and GRIP1/2 to form PDZ domain-based receptor complexes. We will establish the roles of these new PICK1/GRIP interacting proteins, several of which are implicated in neuropsychiatric diseases, in the regulation of AMPA receptor trafficking, synaptic transmission and plasticity. Second, we will determine how both phosphorylation and a novel regulatory mechanism, palmitoylation, dynamically regulate the PDZ domain- based receptor complex, and how these processes regulate receptor trafficking and synaptic plasticity. In complementary experiments, we will use PICK1 and GRIP1/2 knockout mice, phosphorylation site mutant knockin mice, and knockout mice of selected PICK1 and GRIP1/2 interacting proteins to elucidate the role of PDZ domain-based receptor complexes in several forms of plasticity in the hippocampus, cerebellum, somatosensory cortex and the amygdala. Finally, we will analyze behavioral phenotypes, including spatial and motor learning and fear conditioning and extinction of these knockout and knockin mice to determine the role of these regulatory mechanisms in higher brain processes.